The present invention relates to an interconnection structure and a method for designing the same in a semiconductor integrated circuit device with an interconnection structure incorporating air gaps.
Recently, as semiconductor integrated circuits have been miniaturized, the operating speed of transistors has improved, and RC delay time of interconnection has occupied the majority of signal processing time. Accordingly, reduction of wire-to-wire capacitance is most effective in reducing the RC delay, which increases as the wire length is increased and the wiring is miniaturized. In addition, as a semiconductor integrated circuit device has been more densely integrated, the capacitance between wires disposed horizontally to a substrate has been rapidly increased as compared to the capacitance between wires disposed perpendicularly to the substrate. Specifically, the shrinkage rate of a horizontal wire-to-wire space is different from that of a perpendicular wire-to-wire space. If the design rule is reduced by one generation, the wire-to-wire space and the wire width are generally reduced to about 60-70% horizontally and to about 90% perpendicularly. Thus, the more the circuit is miniaturized, the wider the difference of the wire-to-wire spaces between the horizontal and perpendicular directions become. As a result, to suppress the increase in wire-to-wire capacitance caused by miniaturization of the semiconductor integrated circuit, techniques for reducing the dielectric constant between wires are needed.
As a known technique, a semiconductor integrated circuit with an interconnection structure incorporating air gaps that can reduce a signal delay caused by the interconnection to 40% as compared to usual techniques is being used. The interconnection structure incorporating air gaps is not a structure in which every region between wires is intentionally filled up with an insulating film, but a structure in which air gaps are formed within the insulating film by utilizing a plasma CVD film with a low coverage.
By providing such an interconnection structure incorporating air gaps to a semiconductor integrated circuit device, it is possible to reduce a real relative dielectric constant between wires significantly and also to reduce the delay time depending on the wire-to-wire capacitance to 40% as compared to usual techniques.
At present, no method for designing a semiconductor integrated circuit device suitable for the interconnection structure incorporating air gaps has been established. In the interconnection structure incorporating air gaps, if air gaps occupy too much space in each interconnect layer, the strength of the interconnection structure might not be sufficiently secured. On the other hand, in reducing the delay depending on the parasitic capacitance between wires, so long as wires are spaced apart from each other by a certain distance or more, no substantial problem occurs because the parasitic capacitance is reduced.